The relationship of the renin-angiotensin system to regulation of blood pressure, aldosterone secretion and electrolyte metabolism requires further exploration. The regulation of the secretion of mineralocorticoid hormones is less well understood, but they play major roles in metabolism under certain circumstances. In hypertensive patients with similar endocrine symptoms, a means of separating those with and without adrenal tumors is being sought. The circadian rhythm of renin, angiotensin and mineralocorticoids will be studied in normals, patients with and without adrenal tumors and in other disease states (primary aldosteronism, unilateral renal hypertension, isolated hypoaldosteronism, and renal tubular acidosis).